Electronic aircraft gun fire control computer



M 5mm EXUL Jan. 6, 1953 L. J. B. LA cosTE 2,524,510

ELECTRONIC AIRCRAFT GUN FIRE CONTROL COMPUTER Filed March 22, 1945 INVENTOR. LUCIEN J. B. LACOSTE ATTORNEY Patented Jan. 6, 1953 ELECTRONIC AIRCRAFT GUN FIRE CONTROL COMPUTER Lucien J. B. La Coste, Austin, Tex., assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application March 22, 1945, Serial No. 584,238

2 Claims.

This invention relates in general to electrical circuits for the solution of mathematical equations and more particularly to a computer for solving the ballistic problem presented by the firing of airborne guns.

One type of fighter plane carries guns for firing fused shells; the fuse may be adjusted so that the shells will explode at a predetermined time after firing. The plane may also carry apparatus for indicating the azimuth, elevation, and range of the target with respect to the plane.

It is an object of this invention to provide as a meter deflection an indication of the proper range at which to fire the gun so that the explosive shell will explode at the target or in its immediate vicinity.

It is also an object of this invention to provide data for the control of superelevation necessary to compensate for the gravitational drop of the projectile.

Other objects, features, and advantages of this invention will suggest themselves to those skilled in the art and will become apparent from the following description of the invention taken in connection with the accompanying drawing, in which:

Fig. 1 shows a schematic wiring diagram of a computer using the principles of this invention; and

Fig. 2 shows an arrangement of meters 66 and 61 of Fig. 1 for rapid comparison of their respective readings.

The equation which gives the necessary future range at which to fire for the particular shells to be used, is given by the following formula:

R zthe range at which to fire.

V=the muzzle velocity.

S. the indicated air-speed.

H:the altitude.

e=the base of the Naperian logarithm system.

:the air temperature at altitude H.

f1(t):an empirical function obtained from the ballistic data for the shell used.

tzthe fuse time or time of flight of the shell.

R=the time derivative of the actual range.

K1, K2, K3, K4 are constants which satisfy the ballistic equation.

Equation 1 may be rewritten in a simpler form by substituting the expression f2(H,T) for the exponential term in the bracket as shown below:

The formula consists of three terms, the first term of which simply states that the uncorrected firing range or future range is the shell velocity V multiplied by the fuse time t which gives the distance or range, e. g.

The last term is a correction to be added to the first term to compensate for the changing distance between the craft and the target assuming that this distance or present range R is decreasing at a uniform rate (constant velocity). Therefore the velocity R multiplied by the fuse time t is a negative distance and will be subtracted from the first term to give an increase in the range to which the shell should be fired, e. g.

yds. Sec. X sec.)-yds.

The second term is also a correction of the range to compensate for the ballistic effects of air speed, temperature and altitude and is emperically derived. Dimensionally the coefficient ,f1(t) is time in seconds and within the bracket the terms dimensionally express velocity so that again we have,

yds.

sec.

which is to be subtracted from the first term to give the firing range.

The algebraic sum of the three terms is the future of firing range Rs.

To provide a meter reading of future range, voltages proportional to the three terms of the ballistic equation are to be established and algebraically added and applied to the indicating meter 66. Voltage proportional to the present range is applied to meter 61. Thus meter 61 shows present range and when the reading of 66 and 6'! are the same the guns should be fired. The voltage indicating present range may be obtained from other equipment, not shown, carried by the plane. Range determining equipment is well known and any such equipment giving accurate range may be used to give a voltage indicative of range to the equipment described herein.

Referring now more specifically to Fig. 1, potentiometers I2, l3, l4, l6, and I! are ganged together and are adjusted in accordance with t, the fuse time. The arrows indicate increasing t. Considering this adjustment alone it will be evident that the voltage applied to the grid of vacuum tube 62 is increased positively and that to the grid of vacuum tube 43 is decreased if the setting of the fuse time of the shells which are to be used is increased. This is an adjustment which can be made before taking off from the ground and affects the value of t in all three terms of the equation. Potentiometers l8, I9, and 2| are similarly ganged and are adjusted in accordance with S, the indicated air-speed. The arrows indicate increasing S. Thus it will be seen that for this adjustment considered alone the voltage will be increased positively on the grid of tube 43 for increasing air speed. This adjustment would be made in the air and affects the value S in the second term of the equation. A dual adjustment of potentiometer 32, presently to be described, affects the quantities H and T in the second term of the equation. A cnsideration of the circuit in detail as follows:

The first term of Equation 2 is proportional to the voltage between terminal 26 and tap 2'! of potentiometer I2. As the fuse time knob H is rotated, tap 21 varies the voltage proportional to Vt.

The second term of Equation 2 is proportional to the voltage between terminal 26 and tap 26 of potentiometer 2| which is grounded. The first term in the bracket, K1S, appears as a voltage between terminal 26 and junction 29. Added to this is the voltage between junction 29 and tap '28 of potentiometer 2|. This latter voltage represents a fraction l-l-KzS of the potential between junction 29 and tap 3| of potentiometer 32. The tap 3| of potentiometer 32 is adjusted in accordance with the altitude H, while the body 33 of potentiometer 32 is rotated in accordance with temperature T. Potentiometer 32 is made nonlinear to obtain equally spaced scale markings. It is recognized that adjustments for altitude and temperature could both be made by movement of tap 3| of potentiometer 32; however, the described arrangement is preferred because of its greater flexibility. It is obvious that potentiometer 32 may be linear if its scales for altitude and temperature are calibrated accordingly.

In order to maintain constant current through this branch so that adjustments of indicated air speed and altitude Will not interact, potentiometer I9 is so connected as to compensate for variation of potentiometer l8. Additionally, the sum of resistor 24 and a. portion of potentiometer 32 is made small in comparison with the sum of resistors 34 and 36 and potentiometer 2|.

The voltage thus obtained at tap 28 of potentiometer 2| with respect to terminal 26 is modified in accordince with f1(t) by potentiometer |3 which is made non-linear in such a way that the voltage between terminal 26 and junction 31 is proportional to f1(t) Minor errors in the nonlinear Winding of potentiometer |3 are compensated by potentiometer 38.

It is evident that the potential difference between tap 21 of potentiometer l2 and tap 28 of potentiometer 2| represents the difierence between the first and second terms of Equation 2.

This potential diflference is applied directly to grid 4| and through resistors 44 and 46 to cathode 42 of triode 43'. Triode 43 is connected as a non-inverting amplifier, the detailed operation of which will be obvious to those skilled in the art.

The output from triode 43 appears as a voltage across resistor 41 and is applied between grid 48 of triode 49, and the remote end of cathode resistor 52 associated with triode 49.- I o e 4 '4 connected as one-half of a differential cathode follower.

The third term in Equation 2 is obtained as follows: A direct voltage proportional in magnitude to present range R is supplied from other equipment as mentioned above between terminals 50 and 53. From here it is fed to grid 54 of triode 56 which is connected as a conventional resistance-coupled amplifier. The output of this amplifier passes through condenser 51 to potentiometer I6. The time constant of condenser 51 and the parallel combination of potentiometer I 6 and resistor 58 is made small so that the voltage applied to potentiometer I6 is proportional to the time derivative of the actual range. Since the tap 59 of potentiometer I6 is adjusted in accordance with fuse time t, as previously mentioned, the voltage applied to grid 6| of triode 62 represents the product Rt. Cathodes 63 and 64 of tube 5| are connected through milliammeter 66 so that the latter will indicate differences of potential between said cathodes. Thus, the reading of milliammeter 66 represents Rf, the future range at which to fire.

For greater convenience of the gunner, a voltage indicative of actual range which is supplied between terminals 50 and 53 is made to appear as an indication on milliammeter 61. It is preferred that milliammeters 66 and 61 be combined so that both needles have a common pivotal axis and appear on one dial face. The gun is fired when the needle showing range at which to fire and the needle showing actual range coincide.

Referring now more particularly to Fig. 2, meter 61 is the meter indicating present range, and meter 66 is the meter indicating the range at which to fire. These meters are assembled as described above with their needle-axes in alignment. The magnet 68 of meter 66 is inverted with respect to the magnet 69 of milliammeter 61 to allow needles H and T2 of meters 66 and 61, respectively, to be read against scale 13.

Referring again more particularly to Fig. 1, switch 14 is used for calibration purposes by short-circuiting voltage applied to grid 4| of triode 43. With the aircraft stationary on the ground and with a fixed target, the rate of change of actual range is also zero, and milliammeter 66 is then adjusted to zero by adjustment of resistor 52.

Neon lamp T6 is included for the purpose of limiting the voltage between milliammeters 66 and 61, since a high potential between them might cause their indicating needles to be attracted to one another.

The necessary superelevation correction is given by the formula:

where the symbols have the same significance as before. It is seen that this this expression is very similar to Equation 2 for Rr, in that the term in the bracket is identical. However, in Equation 3 the voltage Vt must be added to the voltage between terminal 26 and tap 28 of potentiometer 2| rather than subtracted. Therefore, the direction of rotation of potentiometer 4 is reversed from that of potentiometer 2 so that the voltage between terminal 26 and tap H? of potentiometer I4 represents a constant minus Vt. This causes the potential between taps l5 and 28 to be proportional to the sum of these term as required in Equation 3, potentiometer 11 being so adjustegltas to apply the correct constant of proportiona 1 y.

This resulting potential difference appearing between terminal 60 and ground is fed to the apparatus determining the azimuth and elevation of the target with respect to the plane. Such apparatus is well known and any such apparatus may be used which will supply accurate information as to the azimuth and elevation of the target. The axis of said apparatus is depressed with respect to the axis of the plane by a servo mechanism controlled by said potential difference, so that although said apparatus indicates that the plane and its fixed guns point at the target, the plane is actually pointed up sufliciently to overcome the fall of the projectile due to gravity.

The necessary voltage for operation of the network between junctions 25 and 26 is supplied by a voltage-regulated power supply which is unrounded and can float in accordance with the requirements of this network. In order to aid further in maintaining constant potential between terminals 25 and 26, an additional current branch containing potentiometer I7 is added. This is varied also in accordance with fuse time t in such a manner as to give approximate compensation for the current requirements of the other branches.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as set forth in the appended claims.

The invention claimed:

1. In an aircraft gun fire computer, an electrical circuit for establishing and coordinating a plurality of potentials representing a corresponding plurality of ballistic factors to predict the future range at which the guns should be fired, comprising means for establishing a first direct current potential representing the time rate of change of range, said means including a potentiometer-capacity network, said potentiometer being coupled to the control grid of a vacuum tube, means including a plurality of potentiometers for establishing a second direct current potential representing a summation of the parameters of muzzle velocity, air speed, altitude and temperature, means including an indicating meter for differentially combining said potentials, said means for differentially combining potentials comprising a pair of vacuum tubes, one of which is said vacuum tube, each of said tubes having cathode output load resistors and having said meter connected between the two cathodes, and means comprising a unicontrol of said potentiometers for simultaneously altering all of said potentials in accordance with the fuse time of the shell to be fired.

2. In an aircraft gun fire computer, an electrical circuit for establishing and coordinating a plurality of potentials representing a corresponding plurality of ballistic factors to predict the future range at which the guns should be fired, comprising means including a resistance-potentiometer for establishing a first direct current po- /tential representing the time rate of change of 5 range, means for establishingasecond direct ourrent potential representing a summation of the parameters of muzzle velocity, air speed, altitude and temperature, said last named means including an ungrounded direct current source having a first resistance-potentiometer branch in parallel therewith to provide a potential relative to ground which represents the components of air speed, altitude and temperature, and a second resistance-potentiometer branch in parallel with said first branch for subtracting a potential representing the range correction component of muzzle velocity, thereby to provide said second direct current potential, a third resistance-potentiometer branch in parallel with said potentiometer branches for adding a correction component for muzzle velocity to provide a source representing the ballistic correction for super-elevation of the aircraft's guns, means including an indicating meter for differentially combining said potentials, and means comprising a unicontrol of said potentiometers for simultaneously altering all of said potentials in accordance with the fuse time of the shell to be fired.

LUCIEN J. B. LA COSTE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,387,551 Meitner Aug. 16, 1921 1,573,850 Naiman Feb. 23, 1926 2,009,264 Henderson July 23, 1935 2,190,743 Vance Feb. 20, 1940 2,235,826 Chafee Mar. 25, 1941 2,244,369 Martin June 3, 1941 2,250,708 Herz July 29, 1941 2,276,152 Bull Mar. 10, 1942 2,329,073 Mitchell Sept. 7, 1943 2,399,726 Doyle et a1 May 7, 1946 FOREIGN PATENTS Number Country Date 675,842 Germany May 19, 1939 OTHER REFERENCES Basic Radio by J. Barton Hoag; page 83 (published by D. Van Nostrand Co.)

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